1. Field of the Invention
The present invention is related to a charge pump circuit, and more particularly, to a charge pump circuit with improved reliability.
2. Description of the Prior Art
Commonly used in voltage boosters or voltage multipliers, a charge pump circuit is a two-terminal device which receives a low-level input voltage Vi at an input end, converts the input voltage Vi, and then outputs a high-level output voltage Vo at an output end.
Reference is made to FIG. 1 for a diagram illustrating a prior art charge pump circuit 100. The charge pump circuit 100 includes a first input switch SW1, a second input switch SW2, a first output switch SW3, a second output switch SW4, a charging capacitor C1 and a pumping capacitor C2. The first input switch SW1 is coupled between nodes N1 and N3, while the second input switch SW2 is coupled between nodes N2 and N4. The first output switch SW3 is coupled between the node nodes N3 and N5, while the second output switch SW4 is coupled between nodes N4 and N6. The charging capacitor C1 is coupled between nodes N3 and N4, while the pumping capacitor C2 is coupled between nodes N5 and N6. The charge pump circuit 100 receives the input voltage Vi at node N1 and provides the output voltage Vo at node N5, while a first ground reference voltage Vg1 and a second ground reference voltage Vg2 are respectively received at nodes N2 and N6.
During the boosting period of the prior art charge pump circuit 100, the first input switch SW1 and the second input switch SW2 are turned on, while the first output switch SW3 and the second output switch SW4 are turned off, thereby storing the charges corresponding to the voltage difference between the input voltage Vi and the first ground reference voltage Vg1 into the charging capacitor C1. Next, during the charging period of the prior art charge pump circuit 100, the first output switch SW3 and the second output switch SW4 are turned on, thereby charging the pumping capacitor C2. By appropriately adjusting the value of the second ground reference voltage Vg2, the prior art charge pump circuit 100 can generate the output voltage Vo by boosting the input voltage Vi.
The prior art charge pump circuit 100 performs voltage-boosting by switching the serial/parallel connection of two external capacitors C1 and C2, which occupy large space and add to manufacturing costs. Meanwhile, in thin oxide processes, the prior art charge pump circuit 100 has complicated circuit design and normally requires additional band-gap regulators in order to improve circuit reliability.